Casino dice are called perfect or precision dice because of the way they are made. They are as close to being perfect true cubes as possible, manufactured so each die has an absolutely equal chance of landing on any one of its six faces. Casino dice are specially made to within a tolerance of 0.0005 of an inch. The spots are drilled and filled with material that is equal in weight to the material removed. Usually sides are flush and edges sharp.
They are predominantly transparent red but can come in other colours like green, purple or blue. Some casino dice may have a sanded finish which will make them translucent and not completely transparent. Spots are usually solid but a number of different designs can be found.
It is believed all casino dice should have the same conventional arrangement of faces and spots. They're right handed so that if the 1-spot is face up and the 2-spot is turned to face the left then the 3-spot is to the right of it with all opposing sides adding up to 7. If the 1-spot is face up then the 3-spot runs diagonally up from the left and the 2-spot runs diagonally down from the left. A different orientation of the spots is sometimes used on crooked dice (made to look like casino dice) so a cheat can differentiate them from a set of straight dice.
Since the 1970s, and the move to corporate owned casinos, it has become more and more common for casino dice to have serial numbers printed on them. The number is 3 or 4 numeric digits, possibly with letters and dashes, usually printed on the 6-spot but can be found on any face except the 1-spot. This number denotes the issue and is used to prevent them being switched for crooked dice. Another security check sometimes used is having key letters printed on the underneath of spots which can only be viewed by looking through the transparent die. The casino's name, sometimes location, and/or logo will often be printed on the dice too using a metallic foil. The 1-spot usually bares the casino's name while the 2-spot may have the logo.
The most common size today is 3/4 inch but the size can vary with 5/8 inch and 11/16 inch the next most common sizes.
Casino dice were made of cellulose nitrate, starting around the 1920s, but sometime around the 1950s the manufacturers switched to cellulose acetate which is more durable. Very old casino dice have often started to crystallise and will have turned yellowish around the edges. This crystallisation is caused by age and exposure to moisture and ultra-violet light. A completely crystallised die will disintegrate if pressure is applied.
Casino dice can be readily bought. However, many cheap casino dice are in fact rejects that haven't met the manufacturers standards or used dice that have been cancelled by their casino. Both rejects and used dice will have been defaced in some way. If you want true perfect dice then pay the extra for a stick. A stick is a number of dice that are still in their sealed pack as delivered by the manufacturer.